The Collaborative International Dictionary of English v.0.48:

Spermatheca \Sper`ma*the"ca\, n.; pl. Spermathecae. [NL., from
   Gr. ???? seed + ???? case, or receptacle.] (Zool.)
   A small sac connected with the female reproductive organs of
   insects and many other invertebrates, serving to receive and
   retain the spermatozoa.
   [1913 Webster]